Correct version of Java source specified in maven-compiler-plugin?

For example, setting the source to 1.6 compliance?

<plugin>
   <artifactId>maven-compiler-plugin</artifactId>
   <version>2.0.2</version>
   <configuration>
       <source>1.6</source>
       <target>1.6</target>
   </configuration>
</plugin>

The default JDK defined in eclipse matches what you expect?

In eclipse's preferences check Java > Installed JREs and that the selected one is the version you expect.

The Execution Environment for the expected version is bound in eclipse preferences?

In eclipse's preferences check Java > Installed JREs > Execution Environment has a bound value for compatible JREs.

For example, JavaSE-1.6 should have "perfect match" or an Installed JRE selected as being compatible.

The .claspath specifies the correct Java container?

Open the .classpath file and look for the <classpathentry kind="con" entry.

It should either be using the default JRE:

  <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>

Or it should be a specified execution environment:

  <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.6"/>